Piezoelectric material is material that converts mechanical stress into electrical voltage and vice versa. Traditionally, piezoelectric switches have been appreciated for their durability—a piezoelectric switch may withstand well over 50 million presses.
An excellent piezoelectric sensor is described in published patent application WO 2011/158154. The device described therein comprises in addition to a piezoelectric sensor element also a microcontroller. The piezoelectric sensor element is arranged below the surface of a device in such a manner that, when the device surface is being pressed with a finger, the at least one piezoelectric sensor element is bent, generating a voltage over the at least one piezo electric sensor element. The microcontroller is configured to read the voltage and to output a signal in response to the voltage, after having determined that the measured voltage output from the piezoelectric sensor element is stable enough.